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Connections of the terminal nerve and the olfactory system in two galeomorph sharks: An experimental study using a carbocyanine dye
Author(s) -
Yáñez Julián,
Folgueira Mónica,
Köhler Elisabeth,
Martínez Cristina,
Anadón Ramón
Publication year - 2011
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.22674
Subject(s) - olfactory bulb , biology , terminal nerve , scyliorhinus canicula , olfactory system , anatomy , neuroscience , anterograde tracing , efferent , olfactory nerve , context (archaeology) , central nervous system , diencephalon , afferent , paleontology , biochemistry , fishery , hormone , fish <actinopterygii>
In elasmobranchs the terminal nerve courses separately from the olfactory nerve. This characteristic makes elasmobranchs excellent models to study the anatomy and function of these two systems. Here we study the neural connections of the terminal nerve and olfactory system in two sharks by experimental tracing methods using carbocyanine dyes. The main projections from the terminal nerve system (consisting of three ganglia in Scyliorhinus canicula ) course ipsilaterally to the medial septal nucleus and bilaterally to the ventromedial telencephalic pallial region. Minor terminal nerve projections were also traced ipsilaterally to diencephalic and mesencephalic levels. With regard to the olfactory connections, our results show that in sharks, unlike ray‐finned fishes, the primary olfactory projections are mainly restricted to the olfactory bulb. We also performed tracer application to the olfactory bulb in order to analyze the possible central neuroanatomical relationship between the projections of the terminal nerve and the olfactory bulb. In these experiments labeled neurons and fibers were observed from telencephalic to caudal mesencephalic regions. However, we observe almost no overlap between the two systems at central levels. The afferent and the putatively efferent connections of the dogfish olfactory bulb are compared with those previously reported in other elasmobranchs. The significance of the extratelencephalic secondary olfactory projections is also discussed in a comparative context. J. Comp. Neurol. 519:3202–3217, 2011. © 2011 Wiley‐Liss, Inc.